Introduction

What is Kivy

Kivy is a library for use with the Python programming language. It's a great tool for creating Apps on top of Python code. It is a clean and elegant GUI library. You'll need to know a bit about Python and using the IDLE IDE before you can get going in Kivy. Kivy is object oriented and although a little of the concepts will be touched on in the tutorials if you want to understand more about object oriented programming you will need to research this separately.

This book will focus on Kivy version 1.9.0 with Python 3.4. It is aimed at high-school level coders or complete beginners. It's designed to give you the basics to be able to get started o your own.

Prerequisite Knowledge

These are some resources you can use to learn Python:

Assumed knowledge:

Getting input from a user
Displaying information
Loops, while and for loops
if, else and elif
functions

If you need help installing Kivy there are really good instructions on the Kivy site here.

Hello World!

The first thing you need to do in Kivy is to make a screen appear. While you're working on a PC a command screen will open as well. If you run any print functions (I love those for debugging) they will appear in the command screen (I presume terminal for Apple OS but I don't have one to play with).

Open Python IDLE, then open a new window to create a savable program and copy in the following code:

Code Example 0: Make a screen appear

#!/usr/bin/env python 
from kivy.app import App #We need to import the bits of kivy we need as we need them as importing everything would slow the app down unnecessarily
from kivy.uix.widget import Widget #this is a thing that you want the App to display


class Lesson0(Widget): #this defines the instance of the widget. 
    pass # pass is used to keep the class valid but allow it not to contain anything - At the moment our widget is not defined.


class MyApp(App):
    def build(self):
        return Lesson0()

if __name__ == '__main__': #Documentation suggests that each program file should be called main.py but I think that only matters if you're creating the final App to go onto a phone or tablet we're a long way off from that yet

    MyApp().run() #This must match the name of your App

You need to run this through the kivy batch file in order to get it to run with the kivy library. There is a way around this but it can be confusing and this works pretty well. You can find the full instructions of how to set this up on the kivy website here. It should open an empty black screen.

Now we want to display our "Hello World!" text on the screen. In order to do this we need to use a Label to display text.

Code Example 1: Show "Hello World!"

#!/usr/bin/env python 
from kivy.app import App #We need to import the bits of kivy we need as we need them as importing everything would slow the app down unnecessarily
from kivy.uix.widget import Widget #this is a thing that you want the App to display
from kivy.uix.label import Label #this will import the code for the label in which we want to display Hello World! 


class Lesson1App(App):
    def build(self):
        lbl=Label(text='Hello World!') #lbl is a variable name being assigned the Label definition
        return lbl #This  must match the name of the Widget you want to appear on screen

if __name__ == '__main__': #Documentation suggests that each program file should be called main.py but I think that only matters if you're creating the final App to go onto a phone or tablet we're a long way off from that yet

    Lesson1App().run() #This must match the name of your App